1. Field of the Invention
The present invention relates to a method of removing a heavy metal contained in a semiconductor substrate thinned by a polishing-process.
2. Description of the Related Art
In a manufacturing process of LSI devices, various thermal treatments are applied in various steps depending on configurations of devices. If copper, iron, nickel, chromium or other heavy metal contaminations exist in a semiconductor substrate to be used in the device manufacturing, defects are formed or electric levels are changed in the vicinity of a front surface of the semiconductor substrate in the thermal treatment process, whereby device properties may deteriorate. For this reason, prior to the device manufacturing process, it is necessary to remove these heavy metal elements from the vicinity of the front surface of the semiconductor substrate, where the device is to be formed. Therefore, in manufacturing of the semiconductor devices, gettering techniques have been widely used in which the heavy metal contamination matters intruding into the semiconductor substrate are captured in a portion other than the active region on the front surface side of the semiconductor substrate, whereby deterioration in the device properties can be prevented even if the metal contamination occurs.
The gettering technique is roughly divided into an extrinsic gettering method in which a gettering site for capturing the heavy metal elements is formed on a rear surface of the semiconductor substrate, and an intrinsic gettering method in which the gettering site for capturing the heavy metal elements is formed in the semiconductor substrate.
Of the two methods, the intrinsic gettering method having a high gettering capability is more widely used for gettering the impurities (for example, see JP-08-162406 Laid-Open).
Incidentally, in recent years, it has been demanded that the thickness of the semiconductor substrate be 100 μm or lower due to the miniaturization and reduction in weight of the electronic devices. Accordingly, after the device is formed on the front surface of the semiconductor substrate, the semiconductor substrate is ground from the rear surface side so as to be thinner, such that the thickness thereof is 100 μm or lower. Particularly, after the year 2010, the thickness of the semiconductor substrate is expected to be about 10 μm.